Equifax said its UK systems had not been impacted by the attack, but the information of British consumers may have been accessed because of a process failure in 2016 which saw a “limited amount” of UK data stored on the American system between 2011 and 2016.

It added that the UK consumer data that may have been stolen does not include “any single Equifax business clients or institution”.

It comes after Equifax was ordered by the Information Commissioner’s Office (ICO) to alert British customers after the firm said “criminals” had exploited a website application to access its files.

Lenders rely on the information collected by credit bureaus such as Equifax to help them decide whether to approve financing for homes, cars and credit cards.

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A spokesman for the ICO said: “It is always a company’s responsibility to identify UK victims and take steps to reduce any harm to consumers.

“The Information Commissioner’s Office have been pressing the firm to establish the scale of any impact on UK citizens and have also been engaging with relevant US and UK agencies about the nature of the data breach.

“It can take some time to understand the true impact of incidents like this, and we continue to investigate.

“Members of the public should remain vigilant of any unsolicited emails, texts or calls, even if it appears to be from a company they are familiar with.

“We also advise that people review their financial statements regularly for any unfamiliar activity.

“If any financial details appear to have been compromised, victims should immediately notify their bank or card company. If anyone thinks they may have been a victim of a cyber crime, they should contact Action Fraud.”

Cyber attacks have become an increasing problem for big firms that hold a large amount of customer data.

HSBC and TalkTalk are among the most high-profile British firms to be hit in recent years.